Chromatophores and Color Change 



695 



crab, Uca, which commonly contains black, red, yellow, and white pig- 

 ments in the chromatophore system. 



After removal of the eyestalks from a member of any one of the three 

 groups, the characteristic type of response for that particular group is ob- 

 served. In Group I the animals darken rapidly through complete dispersion 

 of their red and yellow pigment and become quite dark (although never as 

 dark as in normal response to a black background) in an hour or two. They 

 remain in this condition indefinitely. The white pigment undergoes a transi- 

 tory concentration and thereafter exhibits a variable state. Crago, of Group 

 II, most commonly shows a more complex change after eyestalk removal. 

 First there is a transitory darkening of the telson and uropods and a blanch- 



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Fig. 262. Schematic representation of the coloration of eyestalkless crustaceans and 

 state of the dominant chromatophores for each of the three differently responding groups, 

 and of the responses of these to injection of eyestalk or sinus gland extract. Solid arrows 

 indicate extract of total water-soluble material, dashed arrows indicate an alcohol-insoluble 

 fraction, and dotted arrows indicate an alcohol-soluble fraction. From Brown, 1948. 



ing of the remainder of the body, which lasts from one half to one hour. This 

 is followed by a complete blanching of the telson and uropods and darken- 

 ing of the body to an intermediate and mottled coloration. The white pig- 

 ment on the body initially concentrates but then assumes an intermediate 

 condition. The crab, Uca, of Group III, blanches rather quickly after re- 

 moval of its eyestalks, its black chromatophores becoming for the most part 

 punctate, and its white ones commonly broadly reticulate. This condition is 

 maintained without significant change indefinitely. Thus, we see eyestalk 

 removal from various crustaceans resulting in three types of conditions: body- 

 darkening, adoption of an intermediate coloration, and body-blanching. In all 

 three, the animals lost practically all of their responses to changes in color of 

 background or illumination. 



Injection of eyestalk-extract into Group I animals results in a rapid 

 blanching, including dispersal of white pigment. In Group II there is com- 

 plete blanching of both the body and telson and uropods, and also a disper- 



